The present invention is related to a microfiber nonwoven web. More specifically, the invention is related to a web containing superfine microfibers.
Microfiber webs, such as meltblown fiber webs, are well known, and meltblown fiber webs are described in various patents and publications, including Naval Research Laboratory Report 4364, xe2x80x9cManufacture of Super-Fine Organic Fibersxe2x80x9d by V. A. Wendt et al.; Naval Research Laboratory Report 5265, xe2x80x9cAn improved Device for the Formation of Super-Fine Organic fibersxe2x80x9d by K. D. Lawrence et al.; and U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fiber webs, which contain thermoplastic microfibers generally having less than 10 xcexcm in average diameter, are produced by heating a polymer resin to form a melt, extruding the melt through die orifices in a die head to form filaments, directing a stream of heated fluid, usually air, toward the filaments exiting the die orifice to attenuated the filaments, and collecting the filaments on a foraminous surface to form a nonwoven web. Because the filaments are still tacky when they are collected, they form autogenous interfiber bonds to produce an integrated web.
Although conventional meltblown fiber webs contain fine microfibers, there is a need for fiber webs containing finer microfibers. There have been various attempts to reduce the diameter of meltblown fibers. One example of such attempts is reducing the polymer through-put to the die head. However, this direct controlling approach for producing fine meltblown fibers can only be used to reduce the fiber size to a limited extent since after a certain limit the reduction in through-put interrupts the fiber production altogether. Another exemplary process for producing fine meltblown fibers involves the steps of producing bicomponent conjugate meltblown fibers of an island-in-sea configuration and then dissolving the sea component of the meltblown fibers, thereby producing microfibers of the island component. However, the dissolving process is disadvantageous in that it requires a cumbersome dissolving step and it removes substantial portions of the conjugate fibers to produce fine fibers. Consequently, the dissolving process tends to be uneconomical and inefficiently utilizes the component polymers.
Yet another group of exemplary processes known in the art for producing fine fibers is split fiber production processes. However, known split fiber production processes may not be suitable for splitting meltblown fibers. The most widely used split fiber production process is a hydro-needling process, which utilizes a pressurized stream of water to split multicomponent conjugate fibers. In general, the process simultaneously splits and entangles the fibers to form a bonded nonwoven web. However, the hydro-needling process has not been used to produce split meltblown fiber webs since the autogenously bonded meltblown fiber webs, which have very fine breakable fibers and contain substantially uniformly distributed numerous interfiber bonds that restrict fiber movements, are difficult to split with the mechanical splitting process.
There are other fine microfiber webs known in the art, and they include glass microfiber webs. Although superfine glass microfibers can be produced, the glass microfibers are brittle and, thus, are not suitable for applications in which strength properties of the fibers are important.
There remains a need for superfine microfiber webs and a production process for producing the webs.
The present invention provides a web containing superfine microfibers. The web contains a blend of a first group of split microfibers which contains a first polymer component and a second group of split microfibers which contains a second polymer component, wherein at least one of the polymer components is hydrophilic. The invention additionally provides a meltblown fiber web having at least two groups of fibers, wherein each group of the fibers has a distinct cross-sectional configuration.
The invention also provides a splittable meltblown conjugate fiber containing at least two incompatible polymer components that are arranged in distinct segments across the cross-section of the fiber along the fiber length. The fiber can be characterized in that at least one of the polymer components is hydrophilic. In addition, at least one of the component polymers forms distinct unocclusive cross-sectional segments along the length of the fiber such that the segments are dissociable.
The superfine split microfiber web of the present invention exhibits, over conventional meltblown fiber webs, improved properties including improved fiber coverage, strength and textural properties, barrier properties, filtration properties and the like.
The term xe2x80x9csteamxe2x80x9d as used herein refers to both steam and a mixture of steam and air, unless otherwise indicated. The term xe2x80x9caqueous mediumxe2x80x9d as used herein indicates a liquid or gaseous medium that contains water or steam. The term xe2x80x9cfibersxe2x80x9d as used herein refers to both staple length fibers and continuous filaments, unless otherwise indicated. The term xe2x80x9cmulticomponent conjugate fiberxe2x80x9d as used herein refers to a fiber which contains at least two component polymers that are arranged to occupy distinct segments of the cross-section of the fiber along the fiber length.